Arc length indicator



June 30, 1936.

Cum VQLTAGI- W. RICHTER ARC LENGTH INDICATOR Filed June 8, 1 934 Sheets-Sheet l- 32 f INVENTOR.

Walther- Richter Jfine 30, 1936. w. RICHTER 2,045,800

ARC LENGTH INDICATOR Filed June 8, 1934 2 Sheets-Sheet 2 FIG] INVENTOR.

' Walther Richter ATTORNEY.

Patented June 30, 1936 UNITED STATES,

PATENT err-"ice 7 Claims. (curv -s11) This invention provides a simple and eflicient arrangement to indicate to an arc welding operator the relative arc length or voltage of a direct current welding arc, and provides an improved means of amplifying. unidirectional voltages.

Referring to the attached drawings:

Figure l is a diagrammatic view of an electrical system embodying the invention.

Fig. 2 shows a characteristic curve for a vacuum tube such as illustrated in Fig. 1. 9

Fig. 3 is a perspective view of a mode of mounting the comparison lamps of Fig. 1.

Fig. 4 is a perspective view of a welding op erators shield showing a mode of mounting the lamps of Fig. 3 therein.

Figs. 5, 6, and 7 are diagrammatic views of a portion of the apparatus showing modifications thereof.

The are voltage across a welding arc represents very closely the arc length conditions when other conditions of the arc, such for instance, as

the character of the weldrod used, are kept constant. A welding operator usually attempts to which is suitable to his conditions of welding. The present invention provides the operator with a guide whereby he may be informed of even slight deviations from such desired arc length or voltage. The accuracy of the indications thus provided is maintained even though the auxiliary supply voltages to the apparatus vary.

The invention is particularly useful in conjunction with operator-controlled weldrod feeding mechanisms such as disclosed in Patent No.

1,877,969, issued to the present inventor. Referring to Fig. 1, a direct current welding arc I0 is shown as maintained between the electrode II and the'work piece l2 and receiving its supply of current from a source l3; In the present case the electrode has been shown as positive and the work piece negative.

A vacuum tube amplifier is'provided to receive and amplify the desired voltage indications. The amplifier I4, shown,-is-'a screen grid tube which is an eflicient voltage amplifier. Other types of tubes will also function, for example, a three-electrode tube will serve satisfactorily in the practice of the invention.

'50 Grid [5 of tube ll isconnected in a suitable manner through an adjustable resistance l8 and fixed resistances 2| and 23 to one side of the arc voltage, or a voltage proportional thereto, and cathode ii of the tube is connected to the other side of such voltage. The connections to arc.

voltage are preferably made, as illustrated, across an adjustable part I! of the resistance It which in turn is connected in shunt to the are. The voltage drop over-resistance I1 is then proportional to the voltage of the arc and a greater 5 range of adjustment for the apparatus is attained than is the case where the connections to the arc voltage are made directly across the arc.

ment here shown with the welding electrode ll positive and the work l2 negative and a battery I9 or other suitable source of constant potential is inserted between cathode l6 and the work I2 and opposed to the voltage derived from the are 15 in the circuit to provide the desired grid bias range for tube M. In this manner, if for instance, an arc voltage range from 40 to is considered, and the setting of connection 2!! gives a voltage of from 20 to 25, a selection of a volt- 20 age for battery IQ of 26 volts will give a combined voltage range of -1 to -6.

A shunt capacity 22 is provided between resistance 2| and cathode l6 and the resistance 2| and capacity 22 are so proportioned that an appreci- 25 able time constant is introduced in the transmittal-of voltage changes, occurring at the arc, to the grid l5. It is preferred to make this time constant of the order of one to two seconds, thus, insuring that none of the rapid changes of volt- 3 age inherent in the operation of a welding arc 'shall appear at the grid. Bythis means the voltage which is impressed upon the .grid by the arc is a smooth average value of the voltages derived from said are. 35

The above described modes of connecting the arc voltage to the vacuum tube through a voltage divider resistance l8, an opposed fixed voltage, and a voltage averaging arrangement are described in copending application, Serial No. 4 728,886, filed by the present inventor.

In'the present invention a known alternating current voltage variation is impressed between the cathode and grid of the amplifying tube. This is accomplished in Fig. 1, by means of an 4.5 alternating voltage drop produced in resistance 23. To produce said voltage drop through resistance 23-, a connection is made-through condensers 24 and 22 connected on opposite sides of resistance 23 and to a voltage dividing resist- 50 ance 25 which in turn is connected to a source of alternating'voltage consisting of transformer coil26.

Amplifying tube llissupplied with plate circult voltage by means of a standard rectifier unit to It is preferred to employ the polarity arrange- 10 21. The effect upon the resulting plate current flowing between plate 28 and cathode iii of tube l4, due to variations of the voltage applied between grid l5 and cathode i6, is illustrated by the diagram in Fig. 2.

Referring to Fig. 2, curve 29 represents the plate current-grid voltage characteristic of an amplifier tube.. The grid voltages are plotted horizontally, and here cover an indicated range of zero to 5 volts; and the plate current is plotted vertically without the assignment of definite values. The purpose of Fig. 2 is to illustrate the efiect upon the plate current of introducing in the grid circuit an. alternating voltage of known value such as previously described as produced at resistance 23 of Fig. 1. p

Curves 30 and 3| represent such an alternating voltage of approximately one-quarter volt in value introduced upon the grid when the average voltage of the grid is -5 in the case of 30 and lim the case of 3|. By examining the relationships disclosed in Fig. 2 it will be evident that introduction of the one-quarter volt variation at 30, where the average voltage is 5, will produce a relatively small plate current alternating value as shown at 32, whereas the same voltage variation introduced at 3 I, where the average voltage value is l, produces a large alternating of tube l4 passing therethrough has its alternating component applied by a standard amplifying arrangement to a second tube 35. Condenser 36 insures that only the said alternating component of the voltage variation is applied to the grid 31 of tube 35. Transformer 38 transmits an amplified alternating component of the plate current produced in power tube 35. The value of the alternating current transmitted by transformer 38 is a function of the voltage across the arc and in the arrangement shown in Fig. 1 increases as the voltage across the welding arc becomesgreater and decreases as said voltage becomes less.

, The current from transformer 38 passes through lamp 39 which serves as the indicator to the operator of the condition of the arc length. Lamp 40 is a standard with which the operator continually compares the brilliancy of lamp 39. transformer-coil 26 which is also the source of the alternating voltage superimposed upon the average, are derived, unidirectional voltage at the gridbf the voltage amplifying tube l4. -Any small variation of the brilliancy of lamp 40 due to variations in the voltage of source 26 is acparison does not depend upon the constancy of the characteristic of the voltage amplifier tube. For instance, suppose the total plate current in voltage.

Lamp 40 is here connected across the tube l4 were to be'increased, due to a rise by variations other than those of the average arc voltage itself.

Fig. 3 is a perspective viewof a mounting em-' ployed for the lamps utilized to provide a comparison of arc lengths or voltages; Lamps 38 and 40 are mounted in cells 4| and 42, respectively, conveniently arranged beside each other for observation by the operator. A ground glass or similar plate 43 is placed over the openings in the cells.

Fig. 4 illustrates a convenient manner of mounting the comparison lamps in the hood of an operator so that the two illuminated portions of plate 43 are exposed to the interior of the shield and. in range of the operator's vision while he is watching the welding are through the shield.

Figs. 5; 6, and 7 illustrate additional ways of superimposing at the grid l5 an alternating voltage of fixed value upon the unidirectional average voltage value derived from the arc. In Fig. 5, resistance 23 and condenser 24 of Fig. l are omitted from the circuit and transformer 44 interposed having its secondary placed in the position occupied by resistance 23 of Fig. 1.

Fig. 6 is similar to that of Fig. 5 except that instead of putting transformer 44 of Fig. 5 in the place of resistance 23 of Fig. l the source 25 of alternating voltage is connected in series between resistance 2| and grid [5.

In Fig. 7 a way is shown of deriving the superimposed alternating voltage from the standard rectifier employed to supply plate voltage to the tubes. After condenser 22 of Fig. 1 has been dethe magnitude of alternating current which when passed through this condenser will impress thereon the desired magnitude of alternating This current is then passed through condenser 22 by connecting it-across coil 45 of the rectifier through resistance 46 and condenser 41 which are so determined as to supply the required amount of current by means of the voltage existing across coil 45.

It has been found that an average voltage variation of as little as one-tenth volt at the are will cause a noticeable change in brilliancy of light 39. This insures an extremely sensitive indicator for use in controlling of arc voltages or lengths.

While I employ one mode of varying the amplification of a fixed alternating voltage by means of a unidirectional voltage for the purpose of indicating the value of the latter, other known amplifying systems may also be adapted to produce such an alternating current measure for unidirectional voltages.

One skilled in the art may modify the above embodiments without departing from the spirit of the invention herein disclosed and claimed.

I claim:

1. An indicating means for unidirectional voltages comprising means for producing an alternating voltage of predetermined value, means voltages to constitute a measure for said unidirectional voltages and means responsive to said alternating current values to indicate the values of said unidirectional voltages.

2. An indicating means for unidirectional voltages comprising means for producing an alternating voltage of predetermined value, means to amplify said alternating voltage, means to vary the amplification produced by said lastmentioned means in accordance with variations in the unidirectional voltage, and means responsive to said amplified alternating voltage to indicate the value of the unidirectional voltage.

3. An indicating means for unidirectional voltages comprising means for producing an alternating voltage of predetermined value, means to produce alternating current values in response to said predetermined value but modified in accordance with variations in said unidirectional voltages to constitute a measure for said unidirectional voltages. and means including light means responsive to said modified alternating values to indicate directional voltages.

4. A direct current arc length indicator comprising a vacuum tube of at least three electrodes, means for impressing across two of such electrodes an alternating voltage of predetermined value, to produce amplified alternating values of said alternating voltage in the output of said tube, means to vary said amplified alternating values in accordance with the variations in the average voltage of said are, and means I responsive to said amplified alternating values to indicate the length of said are.

5. A direct current arc length indicator comprising an electronic vacuum tube of at least the values of said uni-.

three electrodes, connections whereby an alternating voltage of predetermined value is impressed upon s'aid tube through two of said electrodes to amplify said alternating voltage and produce thereby an alternating component in the output of said tube, additional amplifying means to amplify said alternating component,

means to effect a variation in the values of said amplified alternating component in accordance with the variations of the average voltage of said arc, and means responsive to said amplified alvalue, to produce amplified alternating values of said alternating voltage in the output of said tube, means to vary said amplified alternating values in accordance with the variations in the ternating values to indicate the length of said average voltage of said are, light means responsive to said amplified alternating values to indicate the length of said arm, and a standard comparison light means located with respect to said arc length indicating means for comparison therewith.

7. A unidirectional voltage indicator comprising a vacuum tube having at least an anode, a cathode, and a grid, means for impressing across the grid and cathode an alternating voltage of predetermined value, means for supplying a unidirectional biasing voltage to the grid, which biasing voltage is a function of the unidirectional voltage to be indicated, whereby the gain of the tube is varied in accordance thereto, and means responsive to the alternating voltage component of the output of the tube for indicating the value of the unidirectional voltage.

WALTHER RICHTER. 

